Meanwhile, heat butter and olive oil in a large skillet over medium heat. Add onions and sauté until tender, about 5 minutes. Add garlic and chile pepper flakes then sauté for an additional minute, stirring constantly.

Add crushed tomatoes to the skillet then bring the mixture up to a boil. Turn heat down to low and simmer for 10 minutes, stirring occasionally. Add Italian seasoning, salt and Parmesan cheese, then stir to combine.

Drain cooked pasta and return to the pot. Divide cooked pasta among plates then top with tomato sauce. Garnish with sliced fresh basil, and additional Parmesan cheese, if desired.